\documentclass{article}
\usepackage[pdftex,active,tightpage]{preview}
\setlength\PreviewBorder{2mm}

\usepackage{tikz}
\usetikzlibrary{trees,arrows,positioning, calc}
\tikzstyle{redVertex}  =[draw,fill=red,     circle,minimum size=18pt,inner sep=0pt, text=white]
\tikzstyle{blackVertex}=[draw,fill=black,   circle,minimum size=18pt,inner sep=0pt, text=white]
\tikzstyle{nil}        =[draw,fill=black,rectangle,minimum size=18pt,inner sep=0pt, text=white]

\begin{document}
\begin{preview}
\begin{tikzpicture}[font=\sffamily,very thick,level/.style={sibling distance=80mm/#1}]
\node [blackVertex] (r){2}
      child {
        node [blackVertex] {1}
        child {node [nil] {NIL}}
        child {node [nil] {NIL}}
      }
      child {
        node [blackVertex] {3}
        child {node [nil] {NIL}}
        child {node [nil] {NIL}}
      };
\end{tikzpicture}
\end{preview}
\end{document}
